The present invention resides in the concept of the use of inulin poly(H-sulfate) and salts thereof as inhibitors of the complement system of warm-blooded animals.
Inulin is a polysaccharide closely allied with starch and its structure may be found in the Merck Index, 8th Ed. pp. 568-569 (1968). Inulin itself has been used as a diagnostic agent to test renal function. Recently, inulin has been reported as an activator of the complement system, Infection and Immunity, 11: 273-279 (1975). Poly(H-sulfate)salts of inulin are known. U.S. Pat. Nos. 2,686,779 and 2,697,093 both disclose alkali metal sulfates of inulin and processes for their preparation. As noted in the aforementioned patents, alkali metal sulfates of inulin having varying degrees of sulfation have found application in the chemical industry as thickeners for pastes, as adhesives and as additives for muds used in the drilling of oil wells. Inulin sulphuric acid esters have been reported to be anticoagulants, Arkiv for kemi, mineralogi o. geologi., Bd 24B. No. 5, pp. 1-4 (1946). Inulin sulfate has been reported to possess antilipemic activity, Arch. int. pharmacodyn, XCIX, 334 (1954).
It is known that certain polysaccharides and derivatives thereof process anti-complementary activity. For example, the sulphated polysaccharide heparin, and various salts thereof, have been reported to possess anticomplementary action, J. Infect. Dis., 44: 250-253 (1929); Acta. Med. Scand., 91: 550-554 (1937); Nature, 168: 563-564 (1951); British J. Exp. Path., 33: 327-339 (1952); Int. Congr. Chemother. Proc. 5th (1967), 6, 191-196; and Clin. Res. 21: 877 (1973). Other sulphated polysaccharides, e.g., carrageenin and pentosan polysulphate have been reported as anti-complement agents. Immunology, 8:29 (1965) and Pharmacology, 9:74 (1973).
It has not heretofore been known, however, that the poly(H-sulfate)salts of inulin possess anticomplementary activity. Such is particularly surprising in view of the fact that the free polysaccharide inulin has been reported to acticate the complement system, Infection and Immunity, ibid.
The term "complement" refers to a complex group of proteins in body fluids that, working together with antibodies or other factors, play an important role as mediators of immune, allergic, immunochemical and/or immunopathological reactions. The reactions in which complement participates take place in blood serum or in other body fluids, and hence are considered to be humoral reactions.
With regard to human blood, there are at present more than 11 proteins in the complement system. These complement proteins are designated by the letter C and by number: C1, C2, C3 and so on up to C9. The complement protein C1 is actually an assembly of subunits designated C1q, C1r, and C1s. The numbers assigned to the complement proteins reflect the sequence in which they become active, with the exception of complement protein C4, which reacts after C1 and before C2. The numerical assignments for the proteins in the complement system were made before the reaction sequence was fully understood. The standard reference for nomenclature of complement is Bull. World Health Org., 39, 935-938, (1968). A more detailed discussion of the complement system and its role in body processes can be found in, for example, Scientific American, 229, (No. 5), 54-66 (1973); Medical World News, October 11, 1974, pp. 53-58; 64-66; Harvey Lectures, 66, 75-104 (1972); The New England Journal of Medicine, 287, 489-495; 545-549; 592-596; 642-646 (1972); The John Hopkins Med. J., 128, 57-74 (1971); and Federation Proceedings, 32, 134-137 (1973).
The complement system can be considered to consist of three subsystems, (1) a recognition unit (C1q) which enables it to combine with antibody molecules that have detected a foreign invader; (2) an activation unit, (C1r, C1s, C2, C4, C3); which prepares a site on the neighboring membrane; and (3) an attack unit (C6, C7, C8, C9) which creates a "hole" in the membrane. The membrane attack unit is nonspecific; it destroys invaders only because it is generated in their neighborhood in order to minimize damage to the host's own cells, its activity must be limited in time. This limitation is accomplished partly by the spontaneous decay of activated complement and partly by interference by inhibitors and destructive enzymes. The control of complement, however, is not perfect, and there are times when damage is done to the host's cells. Immunity is therefore a double-edged sword.
Activation of the complement system also accelerates blood clotting. This action comes about by way of the complement-mediated release of a clotting factor from platelets. The biologically active complement fragments and complexes can become involved in reactions that damage the host's cells, and these pathogenic reactions can result in the development of immune-complex ciseases. For example, in some forms of nephritis complement damages the basal membrane of the kidney, resulting in the escape of protein from the blood into the urine. The disease disseminated lupus erythematosus belongs in this category; its symptoms include nephritis, visceral lesions and skin eruptions. The treatment of diphtheria or tetanus with the injection of large amounts of antitoxin sometimes results in serum sickness, an immune-complex disease. Rheumatoid arthritis also involves immune complexes. Like disseminated lupus erythematosus, it is an autoimmune disease, in which the disease symptoms are caused by pathological effects of the immune system in the host's tissues. In summary, the complement system has been shown to be involved with inflammation, coagulation, fibrinolysis, antibody-antigen reactions and other metabolic processes.
In the presence of antibody-antigen complexes the complement proteins are involved in a series of reactions which may lead to irreversible membrane damage if they occur in the vicinity of biological membranes. Thus, while complement constitutes a part of the body's defense mechanism against infection, it also results in inflammation and tissue damage in the immunopathological process. The nature of certain of the complement proteins, suggestions regarding the mode of complement binding to biological membranes and the manner in which complement effects membrane damage are discussed in Annual Review of Biochemistry, 38, 389 (1969).
It has been reported that the known complement inhibitors epsilon-aminocaproic acid, Suramin Sodium and tranexamic acid have been used with success in the treatment of hereditary angioneurotic edema, a disease state resulting from an inherited deficiency or lack of function of the serum inhibitor of the activated first component of complement (C1 inhibitor), The New England Journal of Medicine, 286, 808-812, (1972); Allergol, Et. Immunopath., II, 163-168 (1974); and J. Allergy Clin. Immunol., 53, No. 5, 298-302 (1974).